A long time ago, I was on a boat trip in Indonesia (near Bali) and we stopped for the night at a tiny island privately owned by the tour company. We decided to take a walk around the island one night, and as we walked on the beach we noticed that the sand was starting to light up around our feet with every step. There were some kind of bioluminescent plankton mixed in with the sand. We then tried tossing handfuls of sand out into the water, and wherever it hit the water would light up.

A few days later we had to disembark at night and we took rowboats out from the main ship. The constant agitation of the boats & oars moving through the water left an incredibly bright glowing trail of luminescence in our wake.

Other contenders

Flying over Monterey, CA in the glass-front nose of a B-17

The Saturn V rocket at the Kennedy Space Center

Seeing the northern lights while in the air en-route to Alaska

Hiking in Hawaii (big island) to an active lava flow and then poking at the lava and picking it up with a stick

walking past a scrap yard with a friend on our way home from watching Tombstone at the cinema,talking about the movie and it was Thundering and Lightning(and raining),and Lightning struck down and hit a car about 20-30ft from us.....we both looked at each other and said Holy Shit at the same time and ran all the way home

All i can remember is seeing the lightning fork hitting the car and extending all the way to the heavens,i was only 16 or so at the time(1992-3 ish),and i only thought those type of lightning strikes happened in the movies(maybe Tombstone for one)

Maybe i have seen other things just as cool,but that is the one thing that sticks in my mind,and may of even been the start of realising just how awesome and destructive Nature can be

Also,needs to be noted that in Manchester at least,we very rarely get cool lightning storms...at a place where that is common,i guess it probably happens all the time

I did a night dive off the of the Big Island of Hawaii where Manta Rays are swimming all around you. 15 feet wide animals gliding within inches of your face. It was amazing. Here's a video I took (actually it's my wife filming):

Years ago we had some freezing rain. There was ice everywhere. Once the rain stopped the clouds cleared and it became very sunny. I owned a van at the time and my roomate and I were headed out in the van. The sun had begun to melt the sheet of ice that was on top of my van and when I stopped at a light, the momentum change caused the sheet of ice to slide forward off the top of the van and down in front of the windshield. The ice shattered into 1000's of pieces as it hit the vans hood and the resulting bright sunlight cause a burst of rainbow like colors flashing from the pieces of ice. It was amazing, kind of like someone exploded a rainbow across the hood of my van.

Years ago they used to do Jimmy Doolittle flyovers with B-17s, they would fly around Monterey (were he lived until he died) and one year several of them returned afterwards to the Fresno airport. We went out and watched them come in low over the winery property to land at the airport.

Standing at the Dr.'s shoulder as my little girl was being birthed. She came out sunny side up.(face first, looking up)As she took her first slide ride and came out I shouted its a GIRL!!! the Dr. looked at me and said, "hey, that's my job".But seriously in a life with a ton of "moments" the birth of my 3 children is always at the top.